1. Field of the Invention
The invention relates to a low power radio frequency receiver, a matching transmitter, a communication method for a low power receiver, and an electromagnetic signal.
2. Description of the Related Art
State-of-the-art battery powered medical implants must not only provide the prescribed therapy, but they must also be as small as possible, extremely reliable, and have a long service life. For example, the service life of cardiac pacemakers and implantable cardioverter defibrillators (ICDs) is expected to be seven years or more. Since all electronic devices consume electrical energy, medical implants with batteries that are not readily accessible, or easily replaced, must operate with minimal power consumption. Batteries in medical implants have a small and finite capacity to provide electrical energy, and as such, the operational longevity of devices being powered by them is dependent upon the rate at which the devices consume energy. Since implanted medical devices are required to operate for many years from a limited source of energy, the electronic circuitry in the devices must be designed to operate with minimal power consumption.
Present day medical implants often utilize radio telemetry to communicate patient medical data and implant status to a physician. This telemetry may occur frequently, as in the case of home monitoring applications, or it may occur less frequently, such as during patient follow-up examinations in a physician's office. In any event, the radio telemetry circuitry in the implant consumes battery power, and the hence impacts the longevity of the implant.
In the case of pacemakers and ICDs, the primary purpose of the implant is to regulate a patient's heartbeat and/or provide a life-saving shock to treat ventricular fibrillation. The implant's telemetry function is of secondary importance, and because of this, the battery power consumed by the radio telemetry circuitry must be minimal and have negligible impact on the service life of the implant.
In many battery-powered applications, the architectures of devices may employ special techniques to minimize power consumption. For example, devices may be designed to operate in several different modes, some of which may consume less power than others. Devices may have a “sleep” mode whereby they consume very little power or no power at all, and then one or more operational modes where the devices have more functional capability—at the expense of consuming more power. When operating in this manner to save battery power, the devices may change from one operational mode to another. Changes in operational mode may be determined by a time-sequence under the control of hardware or software. Changes in operational mode may also occur upon reception of a signal, or stimulus from an external device or sensor, or they may result from the reception of radio frequency commands transmitted to the device.
In a battery-powered device that changes operating modes upon the reception of radio frequency commands, the radio receiver in the device must be powered on, and remain on continuously, or nearly continuously, to ensure the device receives commands, and responds appropriately and in a timely fashion. The time of arrival of a transmitted command is usually not know by the device in advance, and so the receiver must be powered on in anticipation that a command may be transmitted to it at any time. As a consequence, the device's radio receiver will continuously consume power from the battery even when commands are not being transmitted to it.
The radio frequency electronics circuitry in a conventional receiver typically consumes a considerable amount of power, and hence the operational longevity of a battery-powered device is significantly reduced as the receiver remains powered on for long periods of time. Because a patient must undergo a surgical procedure to replace an implant when its battery power is nearly depleted, it is highly desirable to minimize the power consumption of radio frequency receivers employed in medical implants.